Tapered silicon nanopores with SiO2 surfaces detect individual proteins faster and more clearly by focusing the electric field and reducing protein sticking.
(Nanowerk Spotlight) Molecular sensing often fails at the point where speed and clarity have to work together. A detector that drives proteins through a nanoscale sensing channel too slowly can lose them to unwanted surface contact. A detector that drives them through too quickly can produce signals too brief or noisy to interpret. Proteins make this balance harder because they differ widely in size, shape, charge, and folding, so the channel must guide them without trapping them.
That problem matters for nanopore sensing, where a molecule passes through a nanometer-scale opening and briefly changes the flow of ions. The electrical disturbance can identify or characterize single molecules, but only if the signal rises above noise and lasts long enough to measure. More recent work on single-molecule protein detection with nanopore sensors has shown the promise of reading proteins electrically, while also exposing the limits of capture, selectivity, and signal interpretation.
In a paper in Advanced Functional Materials (“Sub‐10 nm Silicon‐Based Pyramidal Nanopore Enabling High Performance Single Protein Molecule Detection”), researchers report a silicon-based pyramidal nanopore designed to address both limits at once. The pore narrows to a small tip that concentrates the electric field where sensing occurs. A silicon dioxide (SiO₂) surface lines the pore and helps reduce unwanted protein adsorption. The team also developed a fabrication route that produces uniform arrays with openings below 10 nm, reaching 7 nm.
Design of pyramidal nanopores. (a) Schematic of the design concept combining a pyramidal nanopore with a hydrophilic SiO2 surface. (b) Electric field distribution contour maps of cylindrical and pyramidal nanopores; (c) Variation of current density along the central axis of each nanopore; (d) Snapshots from molecular dynamics simulations of α-syn protein translocation through Si and SiO2 substrates; and (e) Corresponding temporal Variation of interaction forces on Si and SiO2 substrates. (Image: Reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
The design targets a specific trade-off in solid-state nanopores. Cylindrical pores can spread the electric field along the channel, which weakens capture at the most important sensing region. At the same time, many solid surfaces encourage proteins to stick, especially when translocation slows. The new device uses a tapered shape to strengthen the field near the constriction and a hydrophilic oxide surface to discourage contact with the wall.
The researchers first tested whether the shape could produce the expected electrical advantage. Simulations showed that current density increased toward the narrow end of the pyramidal pore, while a cylindrical pore kept a more even distribution. That field focusing should raise the probability that a protein enters the sensing region and produces a readable event. The geometry therefore changes not only the size of the opening, but also how molecules experience the driving field.
The field-focusing shape solved only half of the problem. A protein that reaches the constriction still has to pass through without smearing the measurement by sticking to the wall. The researchers used SiO₂ to change that interaction. In simulations with α-synuclein, the oxide surface helped push the negatively charged protein toward the pore center, reducing direct wall contact. The signal improved because the molecule spent less time fighting the surface.
That surface effect mattered only if the team could build pores small enough to test it. Wet etching can carve silicon into pyramids with atomic-plane precision, but the final opening appears suddenly. Once it breaks through, the same chemistry that created the pore can enlarge it before the process stops. At this scale, a short delay can turn a useful constriction into an oversized hole.
The researchers treated the first sign of ionic current as a stop signal. During the final etching step, they tracked current through the silicon membrane in real time. A sharp rise meant that a through-hole had formed. Instead of relying only on time, temperature, and recipe control, the process responded to the pore itself. That feedback gave the method a way to halt etching before the opening grew beyond the nanoscale range needed for protein detection.
The pore then had to become both smaller and chemically suitable. Thermal oxidation did both jobs in one step. As oxygen converted silicon into SiO₂, the oxide grew inward and narrowed the opening from 28 nm to 7 nm after 8 h. The same reaction also created the hydrophilic lining that helped suppress protein adsorption. Chemical and elemental measurements confirmed that the narrowed surface was SiO₂, not merely reshaped silicon.
With that fabrication sequence in place, the device could test the paper’s central claim: pore size, shape, and surface chemistry should work together rather than trade off against one another. The researchers chose three proteins with different dimensions and biological roles. They used 7 nm pores for α-synuclein, 12 nm pores for immunoglobulin G, and 14 nm pores for ferritin, adjusting the constriction to the target instead of forcing different proteins through one geometry.
α-synuclein provided the most demanding benchmark because its signal can disappear into noise or pass too quickly to resolve. At 200 mV, the 7 nm pore recorded about 600 events with an average dwell time of 0.18 ms and an average current blockade of 0.56 nA. The event rate reached 1.57 events s⁻¹, and the signal-to-noise ratio reached 5.6, exceeding the comparison values the paper reports for silicon nitride, biological, and two-dimensional material nanopores.
Those numbers matter because they describe a balance, not a single performance record. Faster capture helps only if the electrical dips remain distinct. Slower passage helps only until proteins start interacting too much with the wall. The pyramidal oxide pore kept α-synuclein events brief enough for efficient detection, yet clear enough to separate from the baseline. That is the trade-off the design was built to resolve.
The larger proteins showed that the strategy was not limited to α-synuclein. Immunoglobulin G produced clear single-event blockade signals in the 12 nm pore, and ferritin did the same in the 14 nm pore. Both larger targets produced event rates near 1 event s⁻¹ at 200 mV. Work on hybrid nanopore protein sensors points to the same broader lesson: pore architecture can strongly shape capture, sensitivity, and signal quality.
The study does not yet establish a diagnostic device. Real biological samples would add mixtures of proteins, salts, contaminants, and overlapping events that the experiments did not address. The advance lies earlier in the sensing chain. It gives nanopore protein detection a manufacturable silicon route for controlling the opening, shaping the electric field, and reducing surface interference at the same time.
Single-protein nanopore sensing depends on more than the diameter of the opening. It requires a channel that can concentrate the electric field, guide proteins through the sensing region, and limit surface interactions that blur the signal. This work brings those requirements into one silicon-based platform. If future studies extend the method to complex samples and protein classification, pyramidal oxide nanopores could support more consistent label-free measurements for biological research and diagnostic development.
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